The present invention relates to a plate holding apparatus for removing an old plate from a plate cylinder during plate exchange.
A plate holding apparatus of this type is disclosed in Japanese Patent Laid-Open No. 2000-255031(reference 1). The apparatus disclosed in reference 1 has a bracket which is provided in a magazine that collects an old plate and is moved vertically by a driving means, a stationary roller pivotally supported by the bracket, and a movable roller which can come into contact and separate from the stationary roller and is brought into contact opposite to the stationary roller by a biasing means. When the bracket is located at a lower position, the movable roller separates from the stationary roller. When the bracket moves upward, the movable roller is brought into contact opposite to the stationary roller by the biasing force of the biasing means.
In this arrangement, when one end of the plate is released by the plate clamp device of a plate cylinder, the released one end of the plate is fed to a portion between the stationary roller and movable roller. Then, when the bracket moves upward, the movable roller is brought into contact opposite too the stationary roller by the biasing force of the biasing means, so that the two rollers hold one end of the plate. The held plate moves upward as the bracket moves upward, and is discharged.
In the conventional plate holding apparatus described above, when the plate held by the movable roller and stationary roller moves upward, the two rollers are sometimes rotated in directions opposite to the discharge direction by the weight of the plate itself, or by a force that acts in a direction opposite to the plate removing direction due to the frictional force occurring between the plate and the plate clamp when the plate is to be removed from the plate clamp. In this case, the plate deforms to flex so as not to disengage from the plate cylinder, and accordingly the elastic restoration force of the plate may undesirably break the plate holding device. Also, the deformed plate may undesirably enter an ink form roller in contact opposite to the plate cylinder, to damage it.